Abstract
To characterize the specific membrane events underlying the secretion of organic cations in the proximal tubules, the transport of tetraethylammonium (TEA), a prototype cation, has been studied, using brush-border and basolateral membrane vesicles isolated from rat renal cortex. TEA is transported across basolateral membranes via a carrier-mediated system, and this system is stimulated by an inside-negative membrane potential. The transport of TEA across brush-border membranes is driven by an H+ gradient via an electroneutral H+/organic cation antiport system. Aminocephalosporins such as cephalexin (an amphoteric molecule) share a common carrier transport system with TEA in brush-border membranes. The H+/organic cation antiport system is very sensitive to pH (optimum pH 7.0), in contrast to organic anion and D-glucose transport systems. Sulfhydryl groups and histidine residues are essential for the H+/organic cation antiport system in renal brush-border membranes.
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